The scalability and resiliency of connectionless networks is evident from the ubiquity and rapid growth of the Internet. Despite the success of connectionless networks, many service providers use connection-oriented networks for achieving global objectives such as network traffic engineering. This is primarily due to the fact that traffic management in connection oriented networks is operationally simpler than traffic management in connectionless networks. Specifically, service providers often use layer-two connection-oriented networks for achieving global objectives for layer-one connectionless networks. An example is the use of Multi-protocol Label Switching (MPLS) for carrying Internet Protocol (IP) traffic.
In connection-oriented networks, traffic is typically routed from source to destination along pre-determined paths. Since these pre-determined paths may be established and manipulated individually, it is possible to adjust the pre-determined paths to accommodate changing traffic conditions in the network. This accommodation of changing traffic conditions is important for providing a quality of service guarantee for traffic associated with pre-determined paths. Disadvantageously, connection-oriented networks require path establishment for supporting traffic flows originating in the network, making the scaling of connection-oriented networks difficult. Furthermore, failures in the network require explicit establishment of restoration paths, thereby reducing operational ease of connectionless networks.
Use of connection oriented networking, despite ease of deployment and scalability of connectionless networking, is due to the fact that connectionless networks typically use shortest-path, hop-by-hop routing. The use of shortest-path, hop-by-hop routing is well-suited for maintaining best-effort connectivity (e.g., as is done using widely deployed routing protocols such as OSPF), however, maintaining connectivity is not the only objective for service providers. In additional to maintaining connectivity, service providers seek efficient traffic management, effective capacity use (e.g., avoiding congestion on some links while other links remain underutilized), and like objectives. Disadvantageously, while such network-wide objectives are easier to meet with connection-oriented networks than with routing currently employed in connectionless networks, connection-oriented networks are not as scalable as connectionless networks.